Modbus slave: TCP and RTU

[mcauser]

Modbus slave: TCP and RTU

[beyonlo]

Hi!

Any idea?

Thank you in advance!

[mcauser]

Hi @beyonlo

I'm not familiar with the linked library, or how deeply integrated it is with the pycom boards.
Have you reached out to them to see if they are working on a micropython version, or could provide any tips for porting it?

[beyonlo]

Hello @mcauser

Thank you for the reply.

Before answering you I did a research about your comments/suggestions.

I not reached the pycom, but they worked with damien with the ESP32 port, in that time (years ago). Here is the repo about MicroPython running on Pycom boards that are the ESP32 https://github.com/pycom/pycom-micropython-sigfox and here is the doc modules from them https://docs.pycom.io/firmwareapi/pycom/

So, I think that the most things is like on official MicroPython, but some do not have on Pycom MicoPython, like as uasyncio. I'm not a especilist in MicroPython, so I can't to tell much more.

ModBus Slave has two modes: the RTU that use the UART, and, the TCP Server, where this second use the sockets. In my review in the code (with my knowloges) I think that the ModBus RTU will be easier to port/work on official MicroPython because use just UART API. About the ModBus TCP where I would like to use with uasyncio with other applications, I wil need to learning a bit more.

I will to try to study/research/learning a bit more to try fix the errors when running in official MicroPython and try to works and change the API/socket :)

Any other tip will be great.

Ps: anyway, I will also keep looking on the internet if there is a ModBus Slave library for MicroPython :)

Thank you very much.

[brainelectronics]

@beyonlo maybe I'm a few months to late to solve your issue. I had the same topic, so I forked, cleaned and improved the lib of https://github.com/sfera-labs/exo-sense-py-modbus into https://github.com/brainelectronics/micropython-modbus
It's available via upip at https://pypi.org/project/micropython-modbus/

May you're also interested in a ModBus RTU-TCP bridge, so you can e.g. access a RTU slave device through a MicroPython TCP master device, as I did it here: https://github.com/brainelectronics/micropython-modules#modbus-bridge

[beyonlo]

Hello @brainelectronics

@beyonlo maybe I'm a few months to late to solve your issue. I had the same topic, so I forked, cleaned and improved the lib of https://github.com/sfera-labs/exo-sense-py-modbus into https://github.com/brainelectronics/micropython-modbus It's available via upip at https://pypi.org/project/micropython-modbus/

May you're also interested in a ModBus RTU-TCP bridge, so you can e.g. access a RTU slave device through a MicroPython TCP master device, as I did it here: https://github.com/brainelectronics/micropython-modules#modbus-bridge

Great!! Excellent work!

I checked there in github and I noticed two things:
1. I see that the Master and Slave (the RTU and TCP) are all blocking. I mean, that the requests/response will block all application while not finish the operation. Do you have plans to use the uasyncio to have all that working in non-blocking operations (asynchronous mode)? That will be amazing.

I'm not expert, so I do not know what all is needed to be modified to works in all non-blocking, but I have tips that I beliave that you already know:
a) RTU: For non-blocking operations on the RTU (Master and Slave) the use of UART with asyncio.StreamReader() and asyncio.StreamWriter() instead uart.read() and uart.write() I think will be enough.
b) TCP: For the TCP using the uasyncio too, but the socket need to be created as non-blocking I think. Something like this:

import usocket as socket
sock = socket.socket()
sock.setblocking(False)

2. I see that the the RTU do not works with RS485, just with Serial RS232 and pure UART, because I see that has just tx and rx pins, not an extra pin (necessary for RS485), like as enable/disable the extra pin to send/receive data using ModBus protocol over RS485. Do you have plans to add support to works in RS485 too?

Thank you so much the this amazing work!

[brainelectronics]

@beyonlo, thank you for the feedback!

Yes, I'm planning to go for a non blocking Implementations but I don't know when this will happen. Hopefully within the next two weeks, but I can't promise anything. But hey, how about a PR from your side :)

Regarding your missing control pin for modbus, you can either use a module with an built in flow control (simply search for "uart rs485 module") or use the control pin of Serial class that parameter is also available on the ModbusRTU class. It's there but I haven't tested it. It's a leftover from the forked repo.

[beyonlo]

Hello @brainelectronics

Yes, I'm planning to go for a non blocking Implementations but I don't know when this will happen. Hopefully within the next two weeks, but I can't promise anything.

That's great. Do not worry if will be exactly in the next two weeks :) The important is that you already has that intention, because non blocking (for TCP and RTU) is the perfect!

But hey, how about a PR from your side :)

I have no experience enough to do a PR for that, sorry. That example about the non-blocking socket (for the TCP) I get from this project that started to write a MicroPython ModBus protocol, but unfortunatly the author has no intention to finish him :(
https://github.com/eydam-prototyping/mp_modbus/blob/master/mp_modbus_slave.py#L161

For the non blocking on the RTU, that same project has a method that looks like works as non-blocking https://github.com/eydam-prototyping/mp_modbus/blob/master/mp_modbus_slave.py#L109 but that method is not using the asyncio.StreamReader(uart) and asyncio.StreamWriter(uart), just uart.read(), uart.write(), uart.readline() . But accordly with @peterhinch docs (he wrote many docs about uasyncio/non-blocking), is need to use asyncio.StreamReader(uart) and asyncio.StreamWriter(uart) to UART works really as non blocking, like as this example from him https://github.com/peterhinch/micropython-async/blob/master/v3/as_demos/auart.py

Regarding your missing control pin for modbus, you can either use a module with an built in flow control (simply search for "uart rs485 module") or use the control pin of Serial class that parameter is also available on the ModbusRTU class. It's there but I haven't tested it. It's a leftover from the forked repo.

Ohh, sorry, I was looking for a name like as "enable pin". I didn't notice about that name "control pin" (ctrl_pin) - that is, of course, better than "enable" :) Well, with that ctrl_pin, so the modbus are ready to works in RS485. I will test it soon :)

Thank you in advance!